Inkjet printers form printed images using one or more printheads, each one of which includes an array of inkjet ejectors. A controller in the printer operates the ejectors to form printed images that often include both text and graphics and may be formed using one or more ink colors. Some inkjet printers move print media, such as paper sheets, envelopes, or any other article suitable for receiving printed images, on a belt past one or more printheads to receive the ink drops that form the printed image. Many printers that use belts to transport print media use a vacuum plenum and belts that have holes to generate a suction force through the surface of the belt. Each print medium engages a portion of the holes on the surface of the belt and the suction force holds the print medium to the surface of the belt to prevent the print media from slipping or otherwise moving relative to the surface of the belt as the belt moves through the printer. Holding each print medium in place relative to the surface of the moving belt enables the printer to control the timing of the operation of printheads to ensure that the printheads form printed images in proper locations on each print medium and ensures that the print media do not cause jams or other mechanical issues with the printer. In large-scale printer configurations, the belt often carries multiple print media simultaneously.
One problem with belts that carry print media over a vacuum plenum is that the print media do not completely cover every hole on the belt. For example, as a belt carries two or more print media, a gap between sheets of consecutive print media includes holes that are exposed to the vacuum plenum. The suction force of the vacuum plenum draws air through the exposed holes near the edges of the print media, which produces airflow and deviations in pressure in a region around the inter-copy gap. As the inter-copy gap moves past the printheads, the variations in pressure can negatively affect the meniscuses of liquid ink held within the nozzles of the inkjets in the printheads. In some instances, inkjets become inoperable when the variations in air pressure either draw ink from a nozzle in an undesirable manner or push the ink upwards into the nozzle. Either occurrence often results in an inoperable inkjet that can only be returned to service via a cleaning process that requires interruption of operations in the printer. Consequently, improvements to media transport systems that reduce or eliminate the occurrences of inoperable inkjets due to variations in air pressure within a print zone would be desirable.